bug 1132212 - nshttptransction.cpp dont play with data race fire r=sworkman

--HG--
extra : rebase_source : 9c36261b9ce11598664932f2e40693eee735b498

netwerk/protocol/http/NullHttpTransaction.h

@@ -59,10 +59,12 @@ protected:
 private:
   // mCapsToClear holds flags that should be cleared in mCaps, e.g. unset
   // NS_HTTP_REFRESH_DNS when DNS refresh request has completed to avoid
-  // redundant requests on the network. To deal with raciness, only unsetting
+  // redundant requests on the network. The member itself is atomic, but
+  // access to it from the networking thread may happen either before or
+  // after the main thread modifies it. To deal with raciness, only unsetting
   // bitfields should be allowed: 'lost races' will thus err on the
   // conservative side, e.g. by going ahead with a 2nd DNS refresh.
-  uint32_t mCapsToClear;
+  Atomic<uint32_t> mCapsToClear;
   nsHttpRequestHead *mRequestHead;
   bool mIsDone;
   bool mClaimed;

netwerk/protocol/http/nsHttpTransaction.cpp

@@ -102,9 +102,9 @@ nsHttpTransaction::nsHttpTransaction()
     , mPriority(0)
     , mRestartCount(0)
     , mCaps(0)
-    , mCapsToClear(0)
     , mClassification(CLASS_GENERAL)
     , mPipelinePosition(0)
+    , mCapsToClear(0)
     , mHttpVersion(NS_HTTP_VERSION_UNKNOWN)
     , mClosed(false)
     , mConnected(false)

netwerk/protocol/http/nsHttpTransaction.h

@@ -248,16 +248,19 @@ private:
 
     uint16_t                        mRestartCount;        // the number of times this transaction has been restarted
     uint32_t                        mCaps;
-    // mCapsToClear holds flags that should be cleared in mCaps, e.g. unset
-    // NS_HTTP_REFRESH_DNS when DNS refresh request has completed to avoid
-    // redundant requests on the network. To deal with raciness, only unsetting
-    // bitfields should be allowed: 'lost races' will thus err on the
-    // conservative side, e.g. by going ahead with a 2nd DNS refresh.
-    uint32_t                        mCapsToClear;
     enum Classifier                 mClassification;
     int32_t                         mPipelinePosition;
     int64_t                         mMaxPipelineObjectSize;
 
+    // mCapsToClear holds flags that should be cleared in mCaps, e.g. unset
+    // NS_HTTP_REFRESH_DNS when DNS refresh request has completed to avoid
+    // redundant requests on the network. The member itself is atomic, but
+    // access to it from the networking thread may happen either before or
+    // after the main thread modifies it. To deal with raciness, only unsetting
+    // bitfields should be allowed: 'lost races' will thus err on the
+    // conservative side, e.g. by going ahead with a 2nd DNS refresh.
+    Atomic<uint32_t>                mCapsToClear;
+
     nsHttpVersion                   mHttpVersion;
 
     // state flags, all logically boolean, but not packed together into a